Narrow MWD, compositionally optimized ethylene interpolymer composition, process for making the same and article made therefrom

ABSTRACT

A polymer composition comprises at least two polymer components, the first component having an ATREF peak temperature, T peak1 , and a viscosity average molecular weight, M v1 , and the second component having an ATREF peak temperature, T peak2 , and a viscosity average molecular weight, M v2 , wherein the temperature differential between T peak2  and T peak1  decreases with increased composition density and M v1 /M v2  is less than or equal to 1.2. the composition is further characterized as having a M w /M n  of less than or equal to 3.3, an I 10 /I 2 &gt;6.6, and a composition density less than 0.945 gram/cubic centimeter.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 10/247,025, filed Sep. 19, 2002, now U.S. Pat. No.6,683,149; which is a divisional application of U.S. patent applicationSer. No. 09/156,948, filed Sep. 18, 1998, now U.S. Pat. No. 6,469,103,which claims priority to U.S. Provisional Application No. 60/059,555,filed Sep. 19, 1997, all of which are incorporated by referenced hereinin their entirety.

FIELD OF INVENTION

This invention relates to an ethylene interpolymer composition comprisedof at least two dominant polymer components, wherein the composition ischaracterized as having a relatively narrow molecular weightdistribution (MWD) and a variably optimized compositional uniformity.The invention also relates to a process for making such a compositionand fabricated articles made from the novel composition. The novelcomposition exhibits improved and balanced toughness properties, goodprocessibility and improved optical properties and is particularlywell-suited for use in applications such as trash can liners, laminationfilms, oriented shrink film and bags, overwrap films, and heavy dutyshipping bags, especially as blown films.

BACKGROUND OF THE INVENTION

In the manufacture of ethylene interpolymers such as ethyleneinterpolymerized with at least one unsaturated comonomer, a number ofpolymerization methods and procedures are known. For example, singlesite and constrained geometry catalyst systems have been disclosed formanufacturing olefin polymers with high compositional uniformity andrelatively narrow molecular weight distributions.

Variations in the reactor systems used to manufacture ethyleneinterpolymers are also known. For example, while single site catalysissystems are disclosed to provide compositionally uniform, narrow MWDproducts (e.g., EXACT plastomers supplied commercially by Exxon ChemicalCorporation) when employed in a high pressure polymerization system andconversely products with decreased homogeneity with respect to the shortchain branching distribution and a broader molecular weight distribution(e.g., EXCEED resins supplied commercially by Exxon ChemicalCorporation) when employed in a low pressure gas phase polymerizationprocess.

While the art is replete with various products and manufacturingtechniques, the known range of manufacturing capabilities still do notpermit the manufacturing of ethylene interpolymer compositionscharacterized as having high, balanced toughness properties, goodprocessability and improved optical properties. That is, known ethyleneinterpolymer compositions (either as single reactor products, multiplereactor products or polymer blends) do not exhibit the desired balanceof good processability (i.e., sufficient extrusion processingcharacteristics to avoid, for example, excessively high extruderamperage during blown film fabrication with sufficient melt strength topermit, for example, good bubble stability to maximize output rates);balanced tear resistance; high and balanced tensile properties; highdart impact resistance; and low film haze.

The traditional polyethylene solution for achieving improved toughnessproperties involves manufacturing products with narrow molecular weightdistributions as broad molecular weight distributions are known to yieldreduced toughness properties. Beyond providing a narrow molecular weightdistribution, linear polyethylenes are known to provide improvedtoughness properties relative to highly branched LDPE. Further, beyondmerely a narrow molecular weight distribution and a linear polymerbackbone, compositional uniformity has been offered for enhancedtoughness properties. However, while the combination of a narrowmolecular weight distribution, a linear polymer backbone andcompositional uniformity may provide enhanced toughness, thiscombination of polymer properties invariably provides poorprocessability (e.g., excessively high extruder amperage).

In contrast to the combination of a narrow molecular weightdistribution, increased compositional uniformity and a linear polymerbackbone, to achieve the balance of good processability (i.e.,resistance to melt fracture and improved melt strength) and toughnessproperties, Lai et al. disclose in U.S. Pat. No. 5,272,236, thedisclosure of which is incorporated by reference, substantially linearethylene polymers characterized as having narrow molecular weightdistribution, high compositional uniformity and long chain branching.

Other proposed solutions for achieving balanced properties includepolymer blends such as those disclosed by Kale et al. in U.S. Pat. No.5,210,142 and Hazlitt et al. in U.S. Pat. No. 5,370,940, the disclosuresof both of which are incorporated by reference. However, while suchpolymer blends exhibit good handling properties and processability,known polymer blends inevitably exhibit insufficient compositionaluniformity to provide the desired balanced toughness properties.

Fraser et al. in U.S. Pat. No. 4,243,619 disclose a process for makingfilm from a narrow molecular weight distribution ethylene/α-olefincopolymer composition prepared by a Ziegler catalyst system which issaid to exhibit good optical and mechanical properties.

Research Disclosure No. 310163 (Anonymous) teaches blends comprising aZiegler-Natta catalyzed ethylene copolymer and a metallocene catalyzedethylene copolymer fabricated as cast films have improved optical,toughness, heat sealability, film blocking and unwind noise propertieswhen compared to metallocene catalyzed ethylene polymers alone. However,the improvements in tear and ultimate tensile are not shown to bebalanced.

Similarly, Research Disclosure No. 37644 (Anonymous) teaches blends ofZiegler-Natta catalyzed resins and resins made using single sitecatalysis system exhibit superior TD tear resistance and superior MDultimate tensile properties. Hodgson et al. in U.S. Pat. No. 5,376,439also describe film from a polymer blend which is said to have excellentelongation, tensile and impact properties.

WO 98/26000, the disclosure of which is incorporated herein byreference, discloses cast films prepared from interpolymer compositionscomprising a substantially linear ethylene/α-olefin interpolymer and aheterogeneous interpolymer wherein the composition has an I₁₀/I₂ valueof <10 and is characterized as having a log viscosity at 100rad/s≦4.43−0.8×log(I₂) or a log relaxation time>−1.2−1.3×log(I₂). Thereported inventive examples have an average I₂ of 3.65 g/10 minutes andan average I₁₀/I₂ of 7.07 and range in M_(w)/M_(n) from about 2.14 toabout 3.4 and in composition density from about 0.9118 g/cm³ to about0.9188 g/cm³. The reported M_(v1)/M_(v2) ratios and TREF peaktemperature differentials for inventive examples range from about 0.577to about 0.728 and from about 17 to about 24° C., respectively. However,TREF peak temperature differentials are not shown to vary withcomposition density and no density differential between the componentpolymers or component molecular weights are reported in WO 98/26000, noris any property balance or optical improvement discussed or reported.

Hence, in spite of the above disclosures, no known ethylene interpolymercomposition exhibits high, balanced toughness, good processability andgood optical properties. As such, there remains a need for an improvedethylene interpolymer composition, especially for use in blown filmapplications. There is also a need for a process for making an improvedethylene interpolymer composition with the desired property balance.There is also a need for a process for making an improved ethyleneinterpolymer composition wherein the process involves polymerizationusing multiple reactors and the process is characterized by improvedflexibility such that a broad range of product molecular weights and/ordensities can be economically manufactured. There is also a need for ablown film with the desired property balance. These and other objectswill become apparent from the detailed description of the presentinvention provided herein below.

SUMMARY OF THE INVENTION

We have discovered a multicomponent ethylene interpolymer compositionwhich is characterized by a relatively narrow molecular weightdistribution and a variably optimized compositional distribution withrespect to its composition density and short chain branchingdistribution or fractional component crystallinity. The broad aspect ofthe invention is a polymer composition comprising ethyleneinterpolymerized with at least one unsaturated comonomer, wherein thecomposition is characterized as having:

-   -   a) a M_(w)/M_(n) of less than or equal to 3.3, as determined by        gel permeation chromatography (GPC),    -   b) an I₁₀/I₂ in the range of from greater than 6.6 to about 8.2,        as determined in accordance ASTM D-1238, Condition 190° C./2.16        kg and Condition 190° C./10 kg,    -   c) a composition density less than 0.945 gram/cubic centimeter,        as determined according to ASTM-792,    -   d) at least two polymer components, the first component having a        first viscosity average molecular weight, M_(v1), and the second        component having a second viscosity average molecular, M_(v2),        wherein M_(v1)/M_(v2) is less than or equal to 1, as determined        using ATREF-DV, and    -   e) a first ATREF peak temperature, T_(peak1) and a second ATREF        peak temperature, T_(peak2), corresponding to the at least two        components and as determined using analytical temperature rising        elution fraction (ATREF), wherein the temperature differential        between T_(peak2) and T_(peak1), ΔT, decreases with increased        composition density such that ΔT is less than 23° C. at        composition densities greater than or equal to 0.926 g/cm³ and        greater than 13° C. at composition densities less than or equal        to 0.92 g/cm³.

A second aspect of the invention is a polymer composition comprisingethylene interpolymerized with at least one unsaturated comonomer,wherein the composition is characterized as having:

-   -   a) a M_(w)/M_(n) of less than or equal to 3.3, as determined by        gel permeation chromatography (GPC),    -   b) an I₁₀/I₂ ratio greater than 6.6, as determined in accordance        ASTM D-1238, Condition 190° C./2.16 kg and Condition 190° C./10        kg,    -   c) a composition density less than 0.945 gram/cubic centimeter,        as determined according to ASTM-792,    -   d) at least two polymer components, the first component having a        first viscosity average molecular weight, M_(v1), and the second        component having a second viscosity average molecular, M_(v2),        wherein M_(v1)/M_(v2) is in the range of from about 0.6 to about        1.2, as determined using ATREF-DV, and    -   e) a first ATREF peak temperature, T_(peak1) and a second ATREF        peak temperature, T_(peak2), corresponding to the at least two        components and as determined using analytical temperature rising        elution fraction (ATREF), wherein the temperature differential        between T_(peak2) and T_(peak1), ΔT, is equal to or less than        the product of the equation:        ΔT=[5650.842×ρ²]−[11334.5×ρ]+5667.93        wherein ΔT is in degrees Celsius and ρ is composition density in        g/cm³.

In an especially preferred embodiment, the composition is furthercharacterized as having:

-   -   (e) a ΔT which is in the range of from about equal to or greater        than the product of the equation:        ΔT _(lower)=[5650.842×ρ²]−[11334.5×ρ]+5650.27    -    to about equal to or less than the product of the equation:        ΔT _(Upper)=[5650.842×ρ²]−[11334.5×ρ]+5667.93    -    where ΔT is in degrees Celsius and p is composition density in        g/cm³, and    -   (f) a density differential between the density of the second and        first polymer component of less than or equal to 0.028 g/cm³.

Another aspect of the invention is a process for making an ethylenepolymer composition comprised of ethylene interpolymerized with at leastone unsaturated comonomer and characterized as having:

-   -   a) a M_(w)/M_(n) of less than or equal to 3.3, as determined by        gel permeation chromatography (GPC),    -   b) an I₁₀/I₂ in the range of from greater than 6.6 to about 8.2,        as determined in accordance ASTM D-1238, Condition 190° C./2.16        kg and Condition 190° C./10 kg,    -   c) a composition density less than 0.945 gram/cubic centimeter,        as determined according to ASTM-792,    -   d) at least two polymer components, the first component having a        first viscosity average molecular weight, M_(v1), and the second        component having a second viscosity average molecular, M_(v2),        wherein M_(v1)/M_(v2) is less than or equal to 1, as determined        using ATREF-DV, and    -   e) a first ATREF peak temperature, T_(peak1) and a second ATREF        peak temperature, T_(peak2), corresponding to the at least two        components and as determined using analytical temperature rising        elution fraction (ATREF), wherein the temperature differential        between T_(peak2) and T_(peak1), ΔT, decreases with increased        composition density such that ΔT is less than 23° C. at        composition densities greater than or equal to 0.926 g/cm³ and        greater than 13° C. at composition densities less than or equal        to 0.92 g/cm³,        the process comprising continuously operating at least two        polymerization reactors.

The third aspect of the invention is a fabricated article comprising anethylene interpolymer composition which comprises ethyleneinterpolymerized with at least one unsaturated comonomer and ischaracterized as having:

-   -   a) a M_(w)/M_(n) of less than or equal to 3.3, as determined by        gel permeation chromatography (GPC),    -   b) an I₁₀/I₂ in the range of from greater than 6.6 to about 8.2,        as determined in accordance ASTM D-1238, Condition 190° C./2.16        kg and Condition 190° C./10 kg,    -   c) a composition density less than 0.945 gram/cubic centimeter,        as determined according to ASTM-792,    -   d) at least two polymer components, the first component having a        first viscosity average molecular weight, M_(v1), and the second        component having a second viscosity average molecular, M_(v2),        wherein M_(v1)/M_(v2) is less than or equal to 1, as determined        using ATREF-DV, and    -   e) a first ATREF peak temperature, T_(peak1) and a second ATREF        peak temperature, T_(peak2), corresponding to the at least two        components and as determined using analytical temperature rising        elution fraction (ATREF), wherein the temperature differential        between T_(peak2) and T_(peak1), ΔT, decreases with increased        composition density such that ΔT is less than 23° C. at        composition densities greater than or equal to 0.926 g/cm³ and        greater than 13° C. at composition densities less than or equal        to 0.92 g/cm³.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an ATREF-DV curve showing the short chain branchingdistribution as related to the viscosity-average molecular weight(M_(v)) for Inventive Example 1 where ATREF-DV denotes analyticaltemperature rising elufion fractionation coupled with a differentialviscometer for viscosity average molecular weight determination as afunction of elution temperature.

FIG. 2 is an ATREF-DV curve showing the short chain branchingdistribution as related to the viscosity-average molecular weight(M_(v)) for Inventive Example 2.

FIG. 3 is an ATREF-DV curve showing the short chain branchingdistribution as related to the viscosity-average molecular weight(M_(v)) for Comparative Example 3.

FIG. 4 is an ATREF-DV curve showing the short chain branchingdistribution as related to the viscosity-average molecular weight(M_(v)) for Comparative Example 4.

FIG. 5 is an ATREF-DV curve showing the short chain branchingdistribution as related to the viscosity-average molecular weight(M_(v)) for Comparative Example 5.

FIG. 6 is an ATREF-DV curve showing the short chain branchingdistribution as related to the viscosity-average molecular weight(M_(v)) for Inventive Example 6.

FIG. 7 is an ATREF-DV curve showing the short chain branchingdistribution as related to the viscosity-average molecular weight(M_(v)) for Comparative Example 7.

FIG. 8 is an ATREF curve showing the short chain branching distributionas for Comparative Example 8.

DETAILED DESCRIPTION OF THE INVENTION

We have discovered that substantial distinctiveness between dominantpolymer components of an ethylene interpolymer composition results inunbalanced, reduced toughness properties when the composition isconverted into film form. In particular, we discovered that,surprisingly, a composition having a relatively narrow molecular weightdistribution and comparatively high molecular weight can be manufacturedwith high, balanced toughness properties while maintaining goodextrusion processability and optical properties providing itscompositional distribution as determined by analytical temperaturerising elution fractionation (ATREF) is appropriately optimized.

The term “ATREF peak temperature” as used herein refers to the elutiontemperature that corresponds to a peak observed on an ATREF curve asdetermined from temperature rising elution fractionation in the range of20 to 110° C. A peak corresponds to a substantial weight percent ofcrystallized polymer portion based on the total amount of crystallizablepolymer portions for the whole composition. Every ethylene polymercomposition with crystallizable polymer portions will have at least oneATREF peak temperature although the composition may be characterized ashaving measurable crystallized polymer portions at several differentpeak temperatures (i.e., multiple peaks). For purposes of the presentinvention, an ATREF peak is discerned as distinguished from shoulders,humps and doublets. For example, in FIGS. 1 and 2, Inventive Examples 1and 2 are both shown to be characterized by only two ATREF peaks as theLog M_(v) response in FIG. 2 at about 90° C. is not considered toconstitute an ATREF peak. Similarly, the doublet shown in FIG. 4 forcomparative example 4 is also considered to constitute a single ATREFpeak. For the inventive composition, T_(peak1) will be the peakoccurring at the lowest elution temperature and T_(peak2) will be thepeak occurring at the highest elution temperature in the range of20-110° C., although the composition may also have peaks at intermediatetemperatures.

The term “composition density” as used herein means the density of asingle component polymer or a polymer mixture of at least two ethylenepolymers measured in accordance with ASTM D-792. The term “compositiondensity” refers to a solid state density measurement of pellets, film ora molding as distinguished from a melt density determination.

The term “single polymer component” as used herein is distinct from theterm “polymer fraction” which is used in the art in reference to afractionated polymer. Thus, as used herein, a single polymer componentcomprises various polymer fractions and a polymer fraction comprisessmaller polymer fractions (as can be shown using, for example, ATREF).

The term “polymer”, as used herein, refers to a polymeric compoundprepared by polymerizing monomers, whether of the same or a differenttype. The generic term “polymer” thus embraces the terms “homopolymer,”“copolymer,” “terpolymer” as well as “interpolymer.”

The term “interpolymer”, as used herein, refers to polymers prepared bythe polymerization of at least two different types of monomers. Thegeneric term “interpolymer” thus includes the term “copolymers” (whichis usually employed to refer to polymers prepared from two differentmonomers) as well as the term “terpolymers” (which is usually employedto refer to polymers prepared from three different types of monomers).

The term “substantially linear ethylene polymer” is used herein to referspecially to homogeneously branched ethylene polymers that have longchain branching. The term does not refer to heterogeneously orhomogeneously branched ethylene polymers that have a linear polymerbackbone.

For substantially linear ethylene polymers, the long chain branches havethe same comonomer distribution as the polymer backbone, and the longchain branches can be as long as about the same length as the length ofthe polymer backbone to which they are attached. The polymer backbone ofsubstantially linear ethylene polymers is substituted with about 0.01long chain branches/1000 carbons to about 3 long chain branches/1000carbons, more preferably from about 0.01 long chain branches/1000carbons to about 1 long chain branches/1000 carbons, and especially fromabout 0.05 long chain branches/1000 carbons to about 1 long chainbranches/1000 carbons.

Long chain branching is defined herein as a chain length of at least 6carbons, above which the length cannot be distinguished using 13Cnuclear magnetic resonance spectroscopy. The presence of long chainbranching can be determined in ethylene homopolymers by using ¹³Cnuclear magnetic resonance (NMR) spectroscopy and is quantified usingthe method described by Randall (Rev. Macromol. Chem. Phys. C29, V. 2&3,p. 285-297), the disclosure of which is incorporated herein byreference.

Although conventional ¹³C nuclear magnetic resonance spectroscopy cannotdetermine the length of a long chain branch in excess of six carbonatoms, there are other known techniques useful for determining thepresence of long chain branches in ethylene polymers, includingethylene/1-octene interpolymers. Two such methods are gel permeationchromatography coupled with a low angle laser light scattering detector(GPC-LALLS) and gel permeation chromatography coupled with adifferential viscometer detector (GPC-DV). The use of these techniquesfor long chain branch detection and the underlying theories have beenwell documented in the literature. See, e.g., Zimm, G. H. andStockmayer, W. H., J. Chem. Phys., 17, 1301 (1949) and Rudin, A., ModernMethods of Polymer Characterization, John Wiley & Sons, New York (1991)pp. 103-112, both of which are incorporated herein by reference.

A. Willem deGroot and P. Steve Chum, both of The Dow Chemical Company,at the Oct. 4, 1994 conference of the Federation of Analytical Chemistryand Spectroscopy Society (FACSS) in St. Louis, Mo., presented datademonstrating that GPC-DV is a useful technique for quantifying thepresence of long chain branches in substantially linear ethylenepolymers. In particular, deGroot and Chum found that the level of longchain branches in substantially linear ethylene homopolymer samplesmeasured using the Zimm-Stockmayer equation correlated well with thelevel of long chain branches measured using ¹³C NMR.

Further, deGroot and Chum found that the presence of octene does notchange the hydrodynamic volume of the polyethylene samples in solutionand, as such, one can account for the molecular weight increaseattributable to octene short chain branches by knowing the mole percentoctene in the sample. By deconvoluting the contribution to molecularweight increase attributable to 1-octene short chain branches, deGrootand Chum showed that GPC-DV may be used to quantify the level of longchain branches in substantially linear ethylene/octene copolymers.

DeGroot and Chum also showed that a plot of Log(I₂, melt index) as afunction of Log(GPC Weight Average Molecular Weight) as determined byGPC-DV illustrates that the long chain branching aspects (but not theextent of long branching) of substantially linear ethylene polymers arecomparable to that of high pressure, highly branched low densitypolyethylene (LDPE) and are clearly distinct from ethylene polymersproduced using Ziegler-type catalysts such as titanium complexes andordinary homogeneous catalysts such as hafnium and vanadium complexes.

For substantially linear ethylene polymers, the long chain branch islonger than the short chain branch that results from the incorporationof the α-olefin(s) into the polymer backbone. The empirical effect ofthe presence of long chain branching in the substantially linearethylene polymers used in the invention is manifested as enhancedrheological properties which are quantified and expressed herein interms of gas extrusion rheometry (GER) results and/or melt flow, I₁₀/I₂,increases.

The substantially linear ethylene polymers useful in this invention(homopolymers as well as interpolymers) surprisingly have excellentprocessability, even though they have relatively narrow molecular weightdistributions. Substantially linear ethylene polymers have a molecularweight distribution, M_(w)/M_(n), defined by the equation:M _(w) /M _(n)≦(I ₁₀ /I ₂)−4.63.

Even more surprising, the melt flow ratio (I₁₀/I₂) of the substantiallylinear olefin polymers can be varied essentially independently of thepolydispersity index (i.e., molecular weight distribution(M_(w)/M_(n))). This is contrasted with conventional heterogeneouslybranched linear polyethylene resins which have rheological propertiessuch that as the polydispersity index increases, the I₁₀/I₂ value alsoincreases. Also, for the substantially linear ethylene polymers used inthe compositions of the invention, the I₁₀/I₂ ratio indicates the degreeof long chain branching, i.e., the higher the I₁₀/I₂ ratio, the morelong chain branching in the polymer.

The “rheological processing index” (PI) is the apparent viscosity (inkpoise) of a polymer measured by a gas extrusion rheometer (GER). Thegas extrusion rheometer is described by M. Shida, R. N. Shroff and L. V.Cancio in Polymer Engineering Science, Vol. 17, no. 11, p. 770 (1977),and in “Rheometers for Molten Plastics” by John Dealy, published by VanNostrand Reinhold Co. (1982) on page 97-99, both publications of whichare incorporated by reference herein in their entirety. All GERexperiments are performed at a temperature of 190° C., at nitrogenpressures between 5250 to 500 psig using a 0.0296 inch diameter, 20:1L/D die with an entrance angle of 180°. For the substantially linearethylene polymers described herein, the PI is the apparent viscosity (inkpoise) of a material measured by GER at an apparent shear stress of2.15×10⁶ dyne/cm². The substantially linear ethylene polymers describedherein preferably have a PI in the range of about 0.01 kpoise to about50 kpoise, preferably 15 kpoise or less. The substantially linearethylene polymers described herein have a PI less than or equal to 70percent of the PI of a comparative linear ethylene polymer which doesnot contain long chain branching but has about the same I₂ andM_(w)/M_(n) as the substantially linear ethylene polymer being compared.

An apparent shear stress vs. apparent shear rate plot is used toidentify the melt fracture phenomena. According to Ramamurthy in Journalof Rheology, 30(2), 337-357, 1986, above a certain critical flow rate,the observed extrudate irregularities may be broadly classified into twomain types: surface melt fracture and gross melt fracture.

Surface melt fracture occurs under apparently steady flow conditions andranges in detail from loss of specular gloss to the more severe form of“sharkskin”. In this disclosure, the onset of surface melt fracture(OSMF) is characterized at the beginning of losing extrudate gloss atwhich the surface roughness of extrudate can only be detected by 40×magnification. The critical shear rate at onset of surface melt fracturefor the substantially linear ethylene polymers is at least 50 percentgreater than the critical shear rate at the onset of surface meltfracture of a linear ethylene polymer which does not contain long chainbranching but has about the same I₂ and M_(w)/M_(n) as the substantiallylinear ethylene polymer being compared, wherein “about the same” as usedherein means that each value is within 10 percent of the comparativevalue of the comparative linear ethylene polymer.

Gross melt fracture occurs at unsteady flow conditions and ranges indetail from regular (alternating rough and smooth, helical, etc.) torandom distortions. For commercial acceptability, (e.g., in blown filmproducts), surface defects should be minimal, if not absent. Thecritical shear rate at onset of surface melt fracture (OSMF) and onsetof gross melt fracture (OGMF) will be used herein based on the changesof surface roughness and configurations of the extrudates extruded by aGER.

In addition to having a narrow molecular weight distribution,substantially linear ethylene polymers are characterized as having:

-   -   (a) melt flow ratio, I₁₀/I₂ 5.63, and    -   (b) a gas extrusion rheology such that the critical shear rate        at onset of surface melt fracture for the substantially linear        ethylene polymer is at least 50 percent greater than the        critical shear rate at the onset of surface melt fracture for a        linear ethylene polymer, wherein the substantially linear        ethylene polymer and the linear ethylene polymer comprise the        same comonomer or comonomers, the linear ethylene polymer has an        I₂ and M_(w)/M_(n) within ten percent of the substantially        linear ethylene polymer and wherein the respective critical        shear rates of the substantially linear ethylene polymer and the        linear ethylene polymer are measured at the same melt        temperature using a gas extrusion rheometer.

Preferred substantially linear ethylene polymers are furthercharacterized as having a single differential scanning calorimetry, DSC,melting peak between −30° and 150° C.

Substantially linear ethylene polymers are homogeneously branchedethylene polymers and are disclosed in U.S. Pat. No. 5,272,236; U.S.Pat. No. 5,278,272; and U.S. Pat. No. 5,665,800, the disclosures of allthree of which are incorporated herein by reference. Homogeneouslybranched substantially linear ethylene polymers can be prepared via thecontinuous solution, slurry, or gas phase polymerization of ethylene andat least one optional α-olefin comonomer in the presence of aconstrained geometry catalyst, such as the method disclosed in EuropeanPatent Application 416,815-A, which is incorporated herein by reference.The polymerization can generally be performed in any reactor systemknown in the art including, but not limited to, a tank reactor(s), asphere reactor(s), a recycling loop reactor(s) or combinations thereofand the like, any reactor or all reactors operated partially orcompletely adiabatically, nonadiabatically or a combination of both andthe like. Preferably, a continuous solution polymerization process isused to manufacture the substantially linear ethylene polymer used inthe present invention.

The term “heterogeneously branched linear ethylene polymer” is usedherein in the conventional sense in reference to a linear ethyleneinterpolymer having a comparatively low short chain branchingdistribution index. That is, the interpolymer has a relatively broadshort chain branching distribution. Heterogeneously branched linearethylene polymers have a SCBDI less than 50 percent and more typicallyless than 30 percent.

The term “homogeneously branched linear ethylene polymer” is used hereinin the conventional sense to refer to a linear ethylene interpolymer inwhich the comonomer is randomly distributed within a given polymermolecule and wherein substantially all of the polymer molecules have thesame ethylene to comonomer molar ratio. The term refers to an ethyleneinterpolymer that is characterized by a relatively high short chainbranching distribution index (SCBDI) or composition distributionbranching index (CDBI). That is, the interpolymer has a SCBDI greaterthan or equal to 50 percent, preferably greater than or equal to 70percent, more preferably greater than or equal to 90 percent. At higherdegrees of compositional uniformity, homogeneously branched ethylenepolymers can be further characterized as essentially lacking ameasurable high density, high crystallinity polymer portion asdetermined using a temperature rising elution fractionation technique(abbreviated herein as “TREF”).

Homogeneously branched ethylene polymers (i.e. both substantially linearethylene polymers and homogeneously branched linear ethylene polymers)for use in the present invention can be also described as having lessthan 15 weight percent, preferably less than or equal to 10 weightpercent, more preferably less than or equal to 5 weight percent and mostpreferably zero (0) weight percent of the polymer with a degree of shortchain branching less than or equal to 10 methyls/1000 carbons,preferably less than or equal to 5 methyls/1000 carbons. That is, thepolymer contains no measurable high density polymer fraction (e.g.,there is no fraction having a density of equal to or greater than 0.94g/cm³), as determined, for example, using a temperature rising elutionfractionation (TREF) technique and infrared or ¹³C nuclear magneticresonance (NMR) analysis. Conversely, heterogeneously branched ethylenepolymers can be described as having greater than or equal to 15 weightpercent (based on the total weight of the polymer) of the polymer with adegree of short chain branching less than or equal to 10 methyls/1000carbons.

Preferably, the homogeneously branched ethylene polymer is characterizedas having a narrow, essentially single melting TREF profile/curve andessentially lacking a measurable high density polymer portion, asdetermined using a temperature rising elution fractionation technique(abbreviated herein as “TREF”).

SCBDI is defined as the weight percent of the polymer molecules having acomonomer content within 50 percent of the median total molar comonomercontent and represents a comparison of the monomer distribution in theinterpolymer to the monomer distribution expected for a Bernoulliandistribution. The SCBDI of an interpolymer can be readily calculatedfrom TREF as described, for example, by Wild et al., Journal of PolymerScience, Poly. Phys. Ed., Vol. 20, p. 441 (1982), or in U.S. Pat. Nos.4,798,081; 5,008,204; or by L. D. Cady, “The Role of Comonomer Type andDistribution in LLDPE Product Performance,” SPE Regional TechnicalConference, Quaker Square Hilton, Akron, Ohio, October 1-2, pp. 107-119(1985), the disclosures of all which are incorporated herein byreference. However, the preferred TREF technique does not include purgequantities in SCBDI calculations. More preferably, the monomerdistribution of the interpolymer and SCBDI are determined using ¹³C NMRanalysis in accordance with techniques described in U.S. Pat. No.5,292,845; U.S. Pat. No. 4,798,081; U.S. Pat. No. 5,089,321 and by J. C.Randall, Rev. Macromol. Chem. Phys., C29, pp. 201-317, the disclosuresof both of which are incorporated herein by reference.

In analytical temperature rising elution fractionation analysis (asdescribed in U.S. Pat. No. 4,798,081 and abbreviated herein as “ATREF”),the film or composition to be analyzed is dissolved in a suitable hotsolvent (e.g., trichlorobenzene) and allowed to crystallized in a columncontaining an inert support (stainless steel shot) by slowly reducingthe temperature. The column is equipped with both a refractive indexdetector and a differential viscometer (DV) detector. An ATREF-DVchromatogram curve is then generated by eluting the crystallized polymersample from the column by slowly increasing the temperature of theeluting solvent (trichlorobenzene). The ATREF curve is also frequentlycalled the short chain branching distribution (SCBD), since it indicateshow evenly the comonomer (e.g., octene) is distributed throughout thesample in that as elution temperature decreases, comonomer contentincreases. The refractive index detector provides the short chaindistribution information and the differential viscometer detectorprovides an estimate of the viscosity average molecular weight. Theshort chain branching distribution and other compositional informationcan also be determined using crystallization analysis fractionation suchas the CRYSTAF fractionalysis package available commercially fromPolymerChar, Valencia, Spain.

The inventive composition is broadly characterized as having aM_(v1)/M_(v2) in the range of from about 0.6 to about 1.2, preferablyless than or equal to 1.0 and more preferably in the range of from about0.8 to about 1. When M_(v1)/M_(v2) is substantially diverge from 1.0,compositions with improved dart impact resistance may result, however,other toughness properties (i.e., ultimate tensile strength and tearresistance) will invariably be unbalanced when fabricated as blown film.

The inventive composition at a composition density of in the range ofabout 0.92 g/cm³ to about 0.926 g/cm³ is characterized as having anATREF peak temperature differential with respect to the at least twocomponent polymers in the range of about 110° C. to about 22° C.,preferably from about 12° C. to about 20° C. and more preferably fromabout 14° C. to about 18° C. However, persons skilled in the art havingappreciated the present invention, especially the Examples reportedherein below, will recognize that the distinguishing ΔT parameter of thepresent invention varies with composition densities. Accordingly, theinventive composition is generally characterized as having a ΔT whichdecreases with increased composition density such that ΔT is less than23° C. at composition densities greater than or equal to 0.926 g/cm³ andgreater than 13° C. at composition densities less than or equal to 0.92g/cm³. Preferably, however, the inventive composition is characterizedas having a first ATREF peak temperature, T_(peak1) and a second ATREFpeak temperature, T_(peak2), corresponding to the at least twocomponents and as determined using analytical temperature rising elutionfraction (ATREF), wherein the temperature differential between T_(peak2)and T_(peak1), ΔT, is equal to or less than the product of the equation:ΔT=[5650.842×ρ²]−[11334.5×ρ]+5667.93where ΔT is in degrees Celsius and ρ is composition density in g/cm³ andis especially characterized as having a ΔT which is about equal to orgreater than the product of the equation:ΔT _(lower)=[5650.842×ρ²]−[11334.5×ρ]+5650.27and which is about equal to or less than the product of the equation:ΔT _(Upper)=[5650.842×ρ²]−[11334.5×ρ]+5667.93where ΔT is in degrees Celsius and ρ is composition density in g/cm³.That is, the ΔT is in the range of the ΔT_(Lower) and ΔT_(upper).

Preferably, the inventive composition is further characterized as havinga density differential between the densities of the second and firstpolymer components in the range of from about 0 to about 0.028 g/cm³,preferably in the range of from about 0.008 to about 0.026 g/cm³, andmore preferably from about 0.01 to about 0.016 g/cm³.

Preferably, the inventive composition is further characterized as havinga M_(v1)/M_(v2) (i.e. a ratio of the weight average molecular weight ofthe first component polymer to the weight average molecular weight ofthe second component polymer, as determined by GPC which is independentof M_(v1)/M_(v2)) of less than or equal to 1.2, and preferably less thanor equal to 1.

The composition density of the novel composition is generally less than0.945 g/cc, preferably less than 0.94 g/cc and more preferably less than0.938 g/cc, and is especially in the range of from about 0.90 to about0.45 g/cm³, more especially in the range of from about 0.912 to about0.938 g/cm³ and most especially in the range of from about 0.915 toabout 0.935 g/cm³ (as measured in accordance with ASTM D-792).

The molecular weight of polyolefin polymers is conveniently indicatedusing a melt index measurement according to ASTM D-1238, Condition 190°C./2.16 kg (formerly known as “Condition E” and also known as I₂). Meltindex is inversely proportional to the molecular weight of the polymer.Thus, the higher the molecular weight, the lower the melt index,although the relationship is not linear. The overall I₂ melt index ofthe novel composition is preferably in the range of from about 0.001 toabout 200 g/10 minutes, more preferably from about 0.01 to about 20 g/10minutes, most preferably from about 0.01 to about 10 g/10 minutes andespecially when fabricated as blown films is in the range from about 0.1to about 2.2 g/10 minutes, more preferably from about 0.2 and about 1.8g/10 minutes.

Other measurements useful in characterizing the molecular weight ofethylene interpolymer compositions involve melt index determinationswith higher weights, such as, for common example, ASTM D-1238, Condition190□ C/10 kg (formerly known as “Condition N” and also known as I₁₀).The ratio of a higher weight melt index determination to a lower weightdetermination is known as a melt flow ratio, and for measured I₁₀ andthe I₂ melt index values the melt flow ratio is conveniently designatedas I₁₀/I₂.

Broadly, the inventive composition has an I₁₀/I₂ melt flow ratio greaterthan 6.6, more preferably greater than or equal to 6.9, most preferablygreater than or equal to 7.1, and especially in the range of fromgreater than 6.6 to about 8.2, more especially in the range of fromabout 6.7 to about 8.2 and most especially in the range of from about6.8 to about 7.8.

However, in certain preferred embodiments, where maximized opticalproperties and improved processability are desired, at least one polymercomponent will be a substantially linear ethylene polymer (i.e. anethylene polymer made in a continuous polymerization process using aconstrained geometry catalyst system and which results in the so-madepolymer having long chain branching). In such preferred embodiments, theinventive composition itself is preferably further characterized ashaving (in the range of from about 0.01 long chain branches/1,000carbons to about 3 long chain branches/1,000 carbons) greater than orequal to 0.08 long chain branch per 10,000 carbons, more preferablygreater than or equal to 0.1 long chain branch per 10,000 carbons andmost preferably greater than or equal to 0.2 long chain branch per10,000 carbons.

The molecular weight distributions of ethylene polymers are determinedby gel permeation chromatography (GPC) on a Waters 150C high temperaturechromatographic unit equipped with a differential refractometer andthree columns of mixed porosity. The columns are supplied by PolymerLaboratories and are commonly packed with pore sizes of 10³, 10⁴, 10⁵and 10⁶ Å. The solvent is 1,2,4-trichlorobenzene, from which about 0.3percent by weight solutions of the samples are prepared for injection.The flow rate is about 1.0 milliliters/minute, unit operatingtemperature is about 140° C. and the injection size is about 100microliters.

The molecular weight determination with respect to the polymer backboneis deduced by using narrow molecular weight distribution polystyrenestandards (from Polymer Laboratories) in conjunction with their elutionvolumes. The equivalent polyethylene molecular weights are determined byusing appropriate Mark-Houwink coefficients for polyethylene andpolystyrene (as described by Williams and Ward in Journal of PolymerScience, Polymer Letters, Vol. 6, p. 621, 1968) to derive the followingequation:M _(polyethylene) =a*(M _(polystyrene))^(b).In this equation, a=0.4316 and b=1.0. Weight average molecular weight,M_(w), is calculated in the usual manner according to the followingformula: M_(j)=(Σw_(i)(M_(i) ^(j)))^(j); where w_(i) is the weightfraction of the molecules with molecular weight M_(i) eluting from theGPC column in fraction i and j=1 when calculating M_(w) and j=−1 whencalculating M_(n). The novel composition has M_(w)/M_(n) less than orequal to 3.3, preferably less than or equal to 3, and especially in therange of from about 2.4 to about 3.

ATREF analysis can conveniently illuminate several key structuralfeatures of a film or composition. For example, homogeneously branchedethylene polymers such as AFFINITY resins supplied by The Dow ChemicalCompany, ENGAGE resins supplied by Dupont Dow Elastomers, TAFMER resinssupplied by Mitsui Chemical Corporation and EXACT resins supplied byExxon Chemical Corporation are known to exhibit a unique symmetricalsingle elution peak (or homogeneous SCBD). In contrast, ethylenepolymers produced by a conventional Ziegler-Natta catalyst system (suchas, for example, DOLWEX LLDPE resins supplied by The Dow ChemicalCompany) are known to exhibit a bimodal or heterogeneous SCBD with botha broad and a narrow peak eluting at significantly differenttemperatures.

Because the uniqueness of the shape of ATREF curves and elutiontemperatures correspond to polymer densities, ATREF analysis can be usedto fingerprint particular polymers. In particular, for compositionsconsisting of multiple component polymers, by integrating the ATREFcurve, the weight fraction of each component can be convenientlydetermined. Further, the density of component polymers can be determinedfrom ATREF analysis where the composition is known from measurement inaccordance with ASTM D-792. For example, for substantially linearethylene polymers, calibration curves of ATREF elution temperatureversus polymer density provide polymer density is defined by:ρ=0.83494+9.6133×10⁴(T _(e))where T_(e) is the ATREF elution temperature of the polymer. Given theoverall composition density of the composition, the weight fraction ofthe component polymer by integration of the ATREF curve and the polymerdensity of the substantially linear ethylene polymer component, thedensity of the remain component polymer can be conveniently calculated.

To further characterize a polymer composition or mixture, a differentialviscometer may be employed. The output from a differential viscometer isthe viscosity average molecular weight, M_(v), which indicates thevariation in molecular weight as a function of elution volume. The M_(v)response can indicate which component polymer is characterized as havinga higher molecular weight or whether the component polymers arecharacterized as having substantially equivalent molecular weights.

In summary, given the ATREF curve and composition density of a film orcomposition, the weight fraction and polymer densities of the componentpolymers can be calculated. Combining ATREF analysis with a differentialviscometer (ATREF/DV) gives an indication of the relative molecularweights of the component polymers. As such, AFTREF/DV can be used tofingerprint the film or composition of the present invention. The AFREFcurve will show at least two distinct elution peaks given to densitydifferential between the first and second ethylene polymers of theinvention and preferred embodiments will exhibit a single elution peakassociated with the first ethylene polymer component and a secondethylene polymer component having a higher molecular weight than thefirst ethylene polymer component.

A GPC deconvolution technique can be used to determine the melt index ofindividual ethylene polymer components. In this technique, GPC data aregenerated using a Waters 150 C high temperature GPC chromatograph asdescribed herein above. Given empirical elution volumes, molecularweights can be conveniently calculated using a calibration curvegenerated from a series of narrow molecular weight distributionpolystyrene standards. The GPC data should be normalized prior torunning the deconvolution procedure to insure an area of unity under theweight fraction versus log(MW) GPC curve.

For the deconvolution technique, homogeneously branched ethylenepolymers are assumed to follow a Bamford-Tompa molecular weightdistribution, i.e., Eq. [1], $\begin{matrix}{{w_{i}\left( M_{i} \right)} = {{\ln(10)}\frac{M_{i}}{M_{n}}{\exp\left( \left( {- \frac{M_{i}\left( {1 + \xi} \right)}{M_{n}}} \right) \right)} \times \left( \frac{2 + \xi}{\xi} \right)^{1/2} \times {I_{1}\left( \frac{M_{i}{\xi^{1/2}\left( {2 + \xi} \right)}^{1/2}}{M_{n}} \right)}}} & \lbrack 1\rbrack\end{matrix}$where w_(i) is the weight fraction of polymer with molecular weightM_(i), M_(n) is the number average molecular weight, I₁(x) is themodified Bessel function of the first kind of order one, defined by Eq.[2], $\begin{matrix}{{I_{i}(x)} = {\sum\limits_{b}\quad\frac{x^{{2b} + 1}}{2^{{2b} + 1}{b!}{\left( {b + 1} \right)!}}}} & \lbrack 2\rbrack\end{matrix}$and □ is an adjustable parameter which broadens the molecular weightdistribution, as shown in Eq.[3]. $\begin{matrix}{\frac{M_{w}}{M_{n}} = {2 + \xi}} & \lbrack 3\rbrack\end{matrix}$

For the deconvolution technique, heterogeneously branched ethylenepolymers (i.e., polymers manufactured using a Ziegler-Natta catalystsystem) are assumed to follow a log-normal distribution, Eq.[4],$\begin{matrix}{{w_{i}\left( M_{i} \right)} = {\frac{1}{{\beta\left( {2\pi} \right)}^{0.5}}{\exp\left( {{- \frac{1}{2}}\left( \frac{{\log\left( M_{i} \right)} - {\log\left( M_{o} \right)}}{\beta} \right)^{2}} \right)}}} & \lbrack 4\rbrack\end{matrix}$where w_(i) is the weight fraction of polymer with molecular weightM_(i), M_(o) is the peak molecular weight and □ is a parameter whichcharacterizes the width of the distribution. □ was assumed to be afunction of M_(o), as shown in Eq. [5].β=5.70506−2.52383 Log(M _(o))+0.30024(Log(M _(o)))²  [5]

The GPC deconvolution technique involves a four parameter fit, M_(n) and□ for a homogeneously branched ethylene polymer (typically the firstethylene polymer component of the invention), M_(o) for aheterogeneously branched ethylene polymer (preferably the secondcomponent polymer of the invention) and the weight fraction amount ofthe homogeneously branched ethylene polymer. A non-linear curve-fittingsubroutine within SigmaPlot™ supplied by Jandel Scientific (v3.03) isused to estimate these parameters. Given the number average molecularweight (M_(n)), Eq.[3], of the homogeneously branched ethylene polymeror the first ethylene polymer component, its I₁₀/I₂ melt flow ratio andits density, its I₂ melt index can be conveniently calculated using Eq.[6]. $\begin{matrix}{I_{2}^{FCPA} = {\exp\left( {62.782 - {3.8620{{Ln}\left( M_{w} \right)}} - {1.7095{{Ln}\left( \left( \frac{I_{10}}{I_{2}} \right)^{FCPA} \right)}} - {16.310 \times \rho^{FCPA}}} \right)}} & \lbrack 6\rbrack\end{matrix}$where FCPA denotes the ethylene polymer component.

The novel composition can be formed by any convenient method, includingdry blending selected polymer components together and subsequently meltmixing the component polymers in an extruder or by mixing the polymercomponents together directly in a mixer (e.g., a Banbury mixer, a Haakemixer, a Brabender internal mixer, or a single or twin screw extruderincluding a compounding extruder and a side-arm extruder employeddirectly down stream of a polymerization process).

Preferably, the novel composition is manufactured in-situ using anypolymerization method and procedure known in the art (includingsolution, slurry or gas phase polymerization processes at high or lowpressures) provided the operations, reactor configurations, catalysissystems and the like are selected, employed and carried out to indeedprovide the novel composition with its defined combination ofcharacteristics. A preferred method of manufacturing the novelcomposition involves the utilization of a multiple reactorpolymerization system with the various reactors operated in series or inparallel configuration or a combination of both where more than tworeactors are employed. More preferably, the novel composition ismanufactured using a two reactor system wherein the two reactors areoperated in a series configuration.

The inventive composition preferably comprises greater than or equal to40 weight percent of the first component polymer, more preferablygreater than or equal to 45 weight percent of the first componentpolymer and preferably less than or equal to 60 weight percent of thesecond component polymer, more preferably less than or equal to 55weight percent of the second component polymer, based on the totalweight of the composition.

In one especially preferred embodiment of the present invention, theinvention compositions comprises from about 60 to about 75 weightpercent of the first component polymer and from about 5 to about 40weight percent of the second component polymer, especially from about 65to about 70 weight percent of the first component polymer and from about10 to about 30 weight percent of the second component polymer, based onthe total weight of the composition.

In a multiple reactor polymerization system (and especially in a tworeactor system) with reactors configured in series, the polymer split isgenerally greater than or equal to 40 weight percent, preferably in therange of from about 45 to about 80 weight percent, more preferably inthe range of from about 60 weight percent to about 75 weight percent,and most preferably in the range of from about 65 to about 70 weightpercent for the first reactor in the series, based on total amount ofpolymer produced by the polymerization system.

Preferably, the first component (i.e., the polymer componentmanufactured in the first reactor of a series) will be characterized bya lower polymer density and a molecular weight equal to or lower thanthe second (or last) component polymer (i.e. M_(w1)/M_(w2)≦1). To insurethis preference, it may be necessary in a continuous polymerizationsystem to adjust the percent of make-up comonomer feed (e.g., octene) tothe second reactor (or any other reactor other than the first reactor ina series).

If the multiple reactor polymerization comprises two reactors, then thepolymer mass split to the second reactor in the series will generally beequal to or less than 60 weight percent and preferably in the range offrom about 40 weight percent to about 55 weight percent. The firstreactor is a series configuration will typically be that reactorsituated furthest away from the product outlet to finishing operations.

Also, in a preferred embodiment of the invention, a polymerizationsystem consisting of at least one recirculating flow loop reactor andespecially a polymerization system consisting of at least tworecirculating loop reactors operated nonadiabatically (more especiallywith each loop reactor having heat exchange/removal capacities) isemployed to manufacture the novel composition. Such preferredpolymerization systems are as described by Kao et al. in WO 97/36942,the disclosure of which is incorporated herein by reference.

The nonadiabatic polymerization is preferably achieved at a continuousvolumetric heat removal rate equal to or greater than about 400Btu/hour•cubic foot•° F. (7.4 kW/m³•° K.), more preferably, equal to orgreater than about 600 Btu/hour•cubic foot•° F. (11.1 kW/m³•° K.), moreespecially equal to or greater than about 1,200 Btu/hour•cubic foot•° F.(22.2 kW/m³•° K.) and most especially equal to or greater than about2,000 Btu/hour•cubic foot•° F. (37 kW/m³•° K.).

“Volumetric heat removal rate” as used herein is the process heattransfer coefficient, U, in Btu/hour•square foot•° F., multiplied by theheat exchange area, A, in square feet, of the heat exchange apparatusdivided by the total reactor system volume, in cubic feet. One ofordinary skill will recognize that there should be consistencyrespecting whether process side or outside parameters are used as to Uand surface area calculations and determinations. The calculationscontained herein are based on outside surface areas and diameters ofheat exchange tubes, coils, etc. whether or not the reactor mixtureflows through such tubes, coils, etc. or not.

To effectuate nonadiabatic polymerization, any suitable heat exchangeapparatus may be used, in any configuration, including, for example, acooling coil positioned in a polymerization reactor or reactors, ashell-and-tube heat exchanger positioned in a polymerization reactor orreactors wherein the reactor flow stream(s) (also referred to in the artas “reaction mixture”) passes through the tubes, or an entirerecirculating flow loop reactor being designed as a heat exchangeapparatus by providing cooling via a jacket or double piping. In asuitable design, a form of a shell-and-tube heat exchanger can be usedwherein the exchanger housing has an inlet and an outlet for the reactorflow stream and an inlet and outlet for heat transfer media (e.g. water,water/glycol, steam, SYLTHERMO™ material or media supplied by The DowChemical Company under the designation DOWTHERM®). In another design,the reactor flow stream flows through a plurality of heat transfer tubeswithin the heat exchanger housing while the heat transfer media flowsover the tubes' exterior surfaces transferring the heat of reaction orpolymerization from the reactor flow stream. Alternatively, the reactionstream flows through the housing and the heat transfer media flowsthrough the tubes. Suitable heat exchange apparatuses for use in themanufacturing of the novel composition are commercially available items(such as, for example, a static mixer/heat exchanger supplied by Koch)having a tortuous path therethrough defined by the tubes' tubular wallsand/or having solid static interior elements forming an interior webthrough which the reaction mixture flows.

The polymerization reaction to prepared the component polymers may beany reaction type or combination of reactions known in the art,including polymerization by solution, high pressure, slurry and gaspressure. In one preferred embodiment, polymerization is conducted undercontinuous slurry or solution polymerization conditions in at least onereactor to prepared at least one component polymer. In anotherembodiment, the polymerization is conducted under continuous solutionpolymerization conditions in at least one reactor to prepare the firstcomponent polymer. In another embodiment, the polymerization isconducted under continuous slurry polymerization conditions in at leastone reactor to prepare the second component polymer.

It is generally contemplated that any known catalyst system useful forpolymerizing olefins can be used to manufacture the novel compositionincluding, for example, conventional Ziegler-Natta catalyst systems,chromium catalyst systems, so-called single site metallocene catalystsystems such as the monocyclo-pentadienyl transition metal olefinpolymerization catalysts described by Canich in U.S. Pat. No. 5,026,798or by Canich in U.S. Pat. No. 5,055,438, the disclosures of which areincorporated herein by reference, and constrained geometry catalystsystems as described by Stevens et al. in U.S. Pat. No. 5,064,802, thedisclosure of which is incorporated herein by reference. However, inpreferred embodiments, a metallocene catalyst system and conventionalZiegler-Natta catalyst system are used to manufacture the novelcomposition. For preferred embodiments that utilize a polymerizationsystem consisting of at least two reactors in series configuration,preferably a constrained geometry catalyst system is employed in thefirst reactor (or first set of reactors) and a conventionalZiegler-Natta catalyst system is employed in the second reactor (or lastset of reactors).

Catalysts and catalyst systems for use in the invention are described,for example, in EP-A-0 277 003; EP-A-0 277 004; EP-A-0 420 436; PCTInternational Publications WO 91/04257; WO 92/00333; WO 93/08221; and WO93/08199, U.S. Pat. Nos. 3,645,992; 4,076,698; 4,612,300; 4,937,299;5,096,867; 5,055,438; and 5,064,802, the disclosures of all of which areincorporated herein by reference.

Suitable metallocene catalyst components for use in the presentinvention may be derivatives of any transition metal includingLanthanides, but preferably of Group 3, 4, or Lanthanide metals whichare in the +2, +3, or +4 formal oxidation state. Preferred compoundsinclude metal complexes containing from 1 to 3 π-bonded anionic orneutral ligand groups, which may be cyclic or non-cyclic delocalizedπ-bonded anionic ligand groups. Exemplary of such π-bonded anionicligand groups are conjugated or nonconjugated, cyclic or non-cyclicdienyl groups, allyl groups, and arene groups. By the term “π-bonded” ismeant that the ligand group is bonded to the transition metal by meansof a π bond.

Examples of suitable anionic, delocalized π-bonded groups includecyclopentadienyl, indenyl, fluorenyl, tetrahydroindenyl,tetrahydro-fluorenyl, octahydrofluorenyl, pentadienyl, cyclohexadienyl,dihydroanthracenyl, hexahydroanthracenyl, and decahydro-anthracenylgroups, as well as C₁-C₁₀ hydrocarbyl-substituted or C₁-C₁₀hydrocarbyl-substituted silyl substituted derivatives thereof. Preferredanionic delocalized π-bonded groups are cyclopentadienyl,pentamethylcyclopentadienyl, tetramethylcyclopentadienyl,tetra-methylsilylcyclopentadienyl, indenyl, 2,3-dimethylindenyl,fluorenyl, 2-methylindenyl, 2-methyl-4-phenylindenyl,tetrahydro-fluorenyl, octahydrofluorenyl, and tetrahydroindenyl.

Suitable cocatalysts for use herein include but are not limited to, forexample, polymeric or oligomeric aluminoxanes, especially methylaluminoxane or modified methyl aluminoxane (made, e.g., as described inU.S. Pat. Nos. 5,041,584; 4,544,762; 5,015,749; and 5,041,585, thedisclosures of each of which are incorporated herein by reference) aswell as inert, compatible, non-coordinating, ion forming compounds.Preferred cocatalysts are inert, non-coordinating, boron compounds.

The Ziegler catalysts suitable for the preparation of the heterogeneouscomponent of the current invention are typical supported, Ziegler-typecatalysts which are particularly useful at the high polymerizationtemperatures of the solution process. Examples of such compositions arethose derived from organomagnesium compounds, alkyl halides or aluminumhalides or hydrogen chloride, and a transition metal compound. Examplesof such catalysts are described in U.S. Pat. No. 4,314,912 (Lowery, Jr.et al.), U.S. Pat. No. 4,547,475 (Glass et al.), and U.S. Pat. No.4,612,300 (Coleman, III), the teachings of which are incorporated hereinby reference.

Particularly suitable organomagnesium compounds include, for example,hydrocarbon soluble dihydrocarbylmagnesium such as the magnesiumdialkyls and the magnesium diaryls. Exemplary suitable magnesiumdialkyls include particularly n-butyl-sec-butylmagnesium,diisopropylmagnesium, di-n-hexylmagnesium, isopropyl-n-butyl-magnesium,ethyl-n-hexylmagnesium, ethyl-n-butylmagnesium, di-n-octylmagnesium andothers wherein the alkyl has from 1 to 20 carbon atoms. Exemplarysuitable magnesium diaryls include diphenylmagnesium, dibenzylmagnesiumand ditolylmagnesium. Suitable organomagnesium compounds include alkyland aryl magnesium alkoxides and aryloxides and aryl and alkyl magnesiumhalides with the halogen-free organomagnesium compounds being moredesirable.

Among the halide sources which can be employed herein are the activenon-metallic halides, metallic halides, and hydrogen chloride.

Suitable non-metallic halides are represented by the formula R′X whereinR′ is hydrogen or an active monovalent organic radical and X is ahalogen. Particularly suitable non-metallic halides include, forexample, hydrogen halides and active organic halides such as t-alkylhalides, allyl halides, benzyl halides and other active hydrocarbylhalides wherein hydrocarbyl is as defined hereinbefore. By an activeorganic halide is meant a hydrocarbyl halide that contains a labilehalogen at least as active, that is, as easily lost to another compound,as the halogen of sec-butyl chloride, preferably as active as t-butylchloride. In addition to the organic monohalides, it is understood thatorganic dihalides, trihalides and other polyhalides that are active asdefined herein before are also suitably employed. Examples of preferredactive non-metallic halides include hydrogen chloride, hydrogen bromide,t-butyl chloride, t-amyl bromide, allyl chloride, benzyl chloride,crotyl chloride, methylvinyl carbinyl chloride, α-phenylethyl bromide,diphenyl methyl chloride. Most preferred are hydrogen chloride, t-butylchloride, allyl chloride and benzyl chloride.

Suitable metallic halides which can be employed herein include thoserepresented by the formulaMR_(y-a)X_(a)

-   -   wherein:    -   M is a metal of Groups IIB, IIIA or IVA of Mendeleev's Periodic        Table of Elements,    -   R is a monovalent organic radical,    -   X is a halogen,    -   Y has a value corresponding to the valence of M, and    -   a has a value from 1 to y.

Preferred metallic halides are aluminum halides of the formulaAlR_(3-a)X_(a)

-   -   wherein:    -   each R is independently hydrocarbyl as hereinbefore defined such        as alkyl,    -   X is a halogen, and    -   a is a number from 1 to 3.

Most preferred are alkylaluminum halides such as ethylaluminumsesquichloride, diethylaluminum chloride, ethylaluminum dichloride, anddiethylaluminum bromide, with ethylaluminum dichloride being especiallypreferred. Alternatively, a metal halide such as aluminum trichloride ora combination of aluminum trichloride with an alkyl aluminum halide or atrialkyl aluminum compound may be suitably employed.

It is understood that the organic moieties of the aforementionedorganomagnesium, for example, R″, and the organic moieties of the halidesource, for example, R and R′, are suitably any other organic radicalprovided that they do not contain functional groups that poisonconventional Ziegler catalysts.

The magnesium halide can be pre-formed from the organomagnesium compoundand the halide source or it can be formed in situ in which instance thecatalyst is preferably prepared by mixing in a suitable solvent orreaction medium (1) the organomagnesium component and (2) the halidesource, followed by the other catalyst components.

Any of the conventional Ziegler-Natta transition metal compounds can beusefully employed as the transition metal component in preparing thesupported catalyst component. Typically, the transition metal componentis a compound of a Group IVB, VB, or VIB metal. The transition metalcomponent is generally, represented by the formulas:TrX′_(4-q)(OR¹)_(q), TrX′_(4-q)R² _(q), VOX′3 and VO(OR¹)₃.

-   -   wherein:    -   Tr is a Group IVB, VB, or VIB metal, preferably a Group IVB or        VB metal, preferably titanium, vanadium or zirconium,    -   q is 0 or a number equal to or less than 4,    -   X′ is a halogen, and    -   R¹ is an alkyl group, aryl group or cycloalkyl group having from        1 to 20 carbon atoms, and    -   R² is an alkyl group, aryl group, aralkyl group, or substituted        aralkyls.

The aryl, aralkyls and substituted aralkys contain 1 to 20 carbon atoms,preferably 1 to 10 carbon atoms. When the transition metal compoundcontains a hydrocarbyl group, R², being an alkyl, cycloalkyl, aryl, oraralkyl group, the hydrocarbyl group will preferably not contain an Hatom in the position beta to the metal carbon bond.

Illustrative but non-limiting examples of aralkyl groups are methyl,neo-pentyl, 2,2-dimethylbutyl, 2,2-dimethylhexyl; aryl groups such asbenzyl; cycloalkyl groups such as 1-norbornyl. Mixtures of thesetransition metal compounds can be employed if desired.

Illustrative but non-limiting examples of the transition metal compoundsinclude TiCl₄, TiBr₄, Ti(OC₂H₅)₃Cl, Ti(OC₂H₅)Cl₃, Ti(OC₄H₉)₃Cl,Ti(OC₃H₇)₂Cl₂, Ti(OC₆H₁₃)₂Cl₂, Ti(OC₈H₁₇)₂Br₂, and Ti(OC₁₂H₂₅)Cl₃,Ti(O-i-C₃H₇)₄, and Ti(O-n-C₄H₉)₄.

Illustrative but non-limiting examples of vanadium compounds includeVCl₄, VOCl₃, VO(OC₂H₅)₃, and VO(OC₄H₉)₃.

Illustrative but non-limiting examples of zirconium compounds includeZrCl₄, ZrCl₃(OC₂H₅), ZrCl₂(OC₂H₅)₂, ZrCl(OC₂H₅)₃, Zr(OC₂H₅)₄,ZrCl₃(OC₄H₉), ZrCl₂(OC₄H₉)₂, and ZrCl(OC₄H₉)₃.

As indicated above, mixtures of the transition metal compounds may beusefully employed, no restriction being imposed on the number oftransition metal compounds which may be contracted with the support. Anyhalogenide and alkoxide transition metal compound or mixtures thereofcan be usefully employed. The previously named transition metalcompounds are especially preferred with vanadium tetrachloride, vanadiumoxychloride, titanium tetraisopropoxide, titanium tetrabutoxide, andtitanium tetrachloride being most preferred.

Suitable catalyst materials may also be derived from a inert oxidesupports and transition metal compounds. Examples of such compositionssuitable for use in the solution polymerization process are described inU.S. Pat. No. 5,420,090 (Spencer. et al.), the teachings of which areincorporated herein by reference.

The inorganic oxide support used in the preparation of the catalyst maybe any particulate oxide or mixed oxide as previously described whichhas been thermally or chemically dehydrated such that it issubstantially free of adsorbed moisture.

The specific particle size, surface area, pore volume, and number ofsurface hydroxyl groups characteristic of the inorganic oxide are notcritical to its utility in the practice of the invention. However, sincesuch characteristics determine the amount of inorganic oxide to beemployed in preparing the catalyst compositions, as well as affectingthe properties of polymers formed with the aid of the catalystcompositions, these characteristics must frequently be taken intoconsideration in choosing an inorganic oxide for use in a particularaspect of the invention. In general, optimum results are usuallyobtained by the use of inorganic oxides having an average particle sizein the range of 1 to 100 microns, preferably 2 to 20 microns; a surfacearea of 50 to 1,000 square meters per gram, preferably 100 to 450 squaremeters per gram; and a pore volume of 0.5 to 3.5 cm³ per gram;preferably 0.5 to 2 cm³ per gram.

In order to further improve catalyst performance, surface modificationof the support material may be desired. Surface modification isaccomplished by specifically treating the support material such assilica, alumina or silica-alumina with an organometallic compound havinghydrolytic character. More particularly, the surface modifying agentsfor the support materials comprise the organometallic compounds of themetals of Group IIA and IIIA of the Periodic Table. Most preferably theorganometallic compounds are selected from magnesium and aluminumorganometallics and especially from magnesium and aluminum alkyls ormixtures thereof represented by the formulas and R¹MgR² and R¹R²AlR³wherein each of R¹, R² and R³ which may be the same or different arealkyl groups, aryl groups, cycloalkyl groups, aralkyl groups, alkoxidegroups, alkadienyl groups or alkenyl groups. The hydrocarbon groups R¹,R² and R³ can contain between 1 and 20 carbon atoms and preferably from1 to 10 carbon atoms.

The surface modifying action is effected by adding the organometalliccompound in a suitable solvent to a slurry of the support material.Contact of the organometallic compound in a suitable solvent and thesupport is maintained from about 30 to 180 minutes and preferably from60 to 90 minutes at a temperature in the range of 20° to 100° C. Thediluent employed in slurrying the support can be any of the solventsemployed in solubilizing the organometallic compound and is preferablythe same.

Any convenient method and procedure known in the art can be used toprepare a Ziegler-Natta catalyst suitable for use in the presentinvention. One suitable method and procedure is described in U.S. Pat.No. 4,612,300 (the disclosure of which is incorporated herein byreference), in Example P. The described method and procedure involvessequentially adding to a volume of Isopar™ E hydrocarbon, a slurry ofanhydrous magnesium chloride in Isopar™ E hydrocarbon, a solution ofEtAlCl₂ in n-hexane, and a solution of Ti(O-iPr)₄ in Isopar™ Ehydrocarbon, to yield a slurry containing a magnesium concentration of0.166 M and a ratio of Mg/Al/Ti of 40.0:12.5:3.0. An aliquot of thisslurry and a dilute solution of Et₃Al (TEA) are independently pumped intwo separate streams and combined immediately prior to introductionpolymerization reactor system to give an active catalyst with a finalTEA:Ti molar ratio of 6.2:1.

More preferably, the support (e.g. silica and magnesium) to metal (e.g.vanadium, zirconium and titanium) molar ratio and the support surfacearea will be high. In one preferred embodiment, a MgCl₂ supportedtitanium catalyst system is employed to manufacture the second polymercomponent wherein the molar ratio between the magnesium and the titaniumis in the range of 40 moles of Mg to less than 3 moles of Ti, preferably40 moles of Mg to less than 2 moles Ti, more preferably 40.0 moles of Mgto 1.3-1.7 moles of Ti. Most preferably, this MgCl₂ supported titaniumcatalyst system is characterized by the MgCl₂ having a single pore sizedistribution of about 20 to about 25 microns and a specific surface areaof about 400 to about 430 m²/gram.

Preferred dialkylmagnesium precursors for Mg support Ziegler Nattaorganomagnesium catalyst system are butyloctylmagnesium orbutylethylmagnesium which are often stabilized with butykatedhydroxytoluene (BHT) at about 0.5 mol %.

Suitable unsaturated comonomers useful for polymerizing with ethyleneinclude, for example, ethylenically unsaturated monomers, conjugated ornon-conjugated dienes, polyenes, etc. Examples of such comonomersinclude C₃-C₂₀ α-olefins such as propylene, isobutylene, 1-butene,1-hexene, 1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene,1-decene, and the like. Preferred comonomers include propylene,1-butene, 1-hexene, 4-methyl-1-pentene and 1-octene, and 1-octene isespecially preferred. Other suitable monomers include styrene, halo- oralkyl-substituted styrenes, tetrafluoroethylene, vinylbenzocyclobutane,1,4-hexadiene, 1,7-octadiene, and cycloalkenes, e.g., cyclopentene,cyclohexene and cyclooctene. Thus, ethylene interpolymers within thepurview of the present invention include, for example, but are notlimited to, ethylene/propylene interpolymers, ethylene/1-buteneinterpolymers, ethylene/1-pentene interpolymers, ethylene/1-hexeneinterpolymers, ethylene/1-octene interpolymers and ethylene/styreneinterpolymers.

Additives, such as antioxidants (e.g., hindered phenolics, such asIRGANOX™ 1010 or IRGANOX™ 1076 supplied by Ciba Geigy), phosphites(e.g., IRGAFOS™ 168 also supplied by Ciba Geigy), cling additives (e.g.,PIB), SANDOSTAB PEPQ™ (supplied by Sandoz), pigments, colorants,fillers, anti-stats, processing aids, and the like may also be includedin the novel composition or fabricated article. Although generally notrequired, films, coatings and moldings formed from the novel compositionmay also contain additives to enhance antiblocking, mold release andcoefficient of friction characteristics including, but not limited to,untreated and treated silicon dioxide, talc, calcium carbonate, andclay, as well as primary, secondary and substituted fatty acid amides,release agents, silicone coatings, etc. Still other additives, such asquaternary ammonium compounds alone or in combination withethylene-acrylic acid (EAA) copolymers or other functional polymers, mayalso be added to enhance the antistatic characteristics of films,coatings and moldings formed from the novel composition and permit theuse of the composition in, for example, the heavy-duty packaging ofelectronically sensitive goods.

The fabricated articles of the invention (such as, for example, but notlimited to, a film, film layer, fiber, molding, sheet, pouch, bag, sack,tube and coating) may further include recycled and scrap materials anddiluent polymers to provide, for example, multi-polymer blends to theextent that the desired property balanced is maintained. Exemplarydiluent materials include, for example, elastomers (e.g., EPDM, EPR,styrene butadiene block polymer such as styrene-isoprene-styrene,styrene-butadiene, styrene-butadiene-styrene, styrene-ethylene-styreneand styrene-propylene-styrene), natural and synthetic rubbers andanhydride modified polyethylenes (e.g., polybutylene and maleicanhydride grafted LLDPE and HDPE), high density polyethylene (HDPE),medium density polyethylene (MDPE), heterogeneously branched ethylenepolymers (e.g., ultra or very low density polyethylene and linear lowdensity polyethylene) and homogeneously branched ethylene polymers(e.g., substantially linear ethylene polymers) as well as with highpressure polyethylenes such as, for example, low density polyethylene(LDPE), ethylene/acrylic acid (EAA) interpolymers, ethylene/vinylacetate (EVA) interpolymers and ethylene/methacrylate (EMA)interpolymers, and combinations thereof.

The fabricated article of the invention may find utility in a variety ofapplications. Suitable applications are thought to include, for example,but are not limited to, monolayer packaging films; multilayer packagingstructures consisting of other materials such as, for example, biaxiallyoriented polypropylene or biaxially oriented ethylene polymer for shrinkfilm and barrier shrink applications; packages formed via form/fill/sealmachinery; peelable seal packaging structures; cook-in food packages;compression filled packages; heat seal films and packages for foodpackaging, snacks, grains, cereals, cheeses, frozen poultry and frozenproduce; cast stretch films; monolayer shrink film; heat sealablestretch wrap packaging film; ice bags; foams; molded articles;bag-n-box; fresh cut produce packaging; fresh red meat retail packaging;liners and bags such as, for example, cereal liners, grocery/shoppingbags, and especially heavy-duty shipping sacks and trash can liners(bags) where higher levels of downgauging are now possible due to theimproved toughness properties exhibited by the fabricated article of theinvention.

The fabricated article of the invention can be prepared by anyconvenient method known in the art. Suitable methods include, forexample, lamination and coextrusion techniques or combinations thereof,blown film; cast film; extrusion coating; injection molding; blowmolding; thermoforming; profile extrusion, pultrusion; calendering; rollmilling; compression molding; rotomolding; injection blow molding; andfiber spinning and combinations thereof and the like. Preferably,however, the novel composition is fabricated into a blown film for suchuses as packaging, liner, bag or lamination applications, especiallylaminating films.

The fabricated article of the invention can be of any thickness requiredor desired for the intended end-use application. In particular, thenovel film of the invention can be of any suitable film thickness,however, practitioners will appreciate the significant downgauging maybe possible due to the high, balanced toughness properties of the novelfilm. For example, heavy duty shipping sacks typically have filmthicknesses greater than 3 mils, especially greater than 7 mils.

EXAMPLES

The following examples are provided for the purpose of explanation andare not intended to limit the present invention in any way.

In an evaluation to investigate the comparative toughness and opticalproperties of various ethylene interpolymer compositions, severalethylene/1-octene copolymers were obtained. For this investigation,Inventive Examples 1, 2 and 6 and comparative examples 5 and 7 weremanufactured using a non-adiabatic, continuous solution polymerizationsystem consisting of two recirculating loop reactors configured inseries. The process conditions employed in the manufacturing ofInventive Example 1 are provided in Table 1. Process conditions similarto those employed for Inventive Example 1 where also employed in themanufacture of Inventive Examples 2 and 6. The process conditions forcomparative examples 5 and 7 were also similar to those employed forInventive Example 1, except make-up comonomer was feed to the first loopreactor for the comparative examples. It is surprising that this processdifference provides an optimized composition distribution for theinventive examples since the second reactor provides the higher densitypolymer component of the inventive examples. That is, the comonomerincorporation does not lower the polymer density as ordinarily expected,but instead provides an optimized compositional distribution thatresults in balanced toughness properties and improved opticalproperties.

Comparative examples 3, 4 and 8 were manufactured in a singlerecirculating loop reactor. For comparative examples 3 and 8, aconventional Ziegler-Natta catalyst system was employed under continuoussolution polymerization conditions. Comparative example 4, wasmanufactured using a constrained geometry catalyst system according tomethods and procedures described U.S. Pat. No. 5,272,236; U.S. Pat. No.5,278,272; and U.S. Pat. No. 5,665,800.

TABLE 1 Inv. Ex 1 Flow Loop Rx1 Flow Loop Rx2 Process 121 200Temperature, ° C. Process Pressure, 535 535 psig Polymer 16.6 21.9Concentration wt. % C₂ Conversion, % 77.5 86.1 (92.2) (overall)Solvent/C₂ feed ratio 4.5 2.8 Solvent flow, lbs./hr 653 316 C₂ flow,lbs./hr 145 113 Make-up C₈ flow, 0 24 lbs./hr Fresh Hydrogen ˜1000 ˜2000flow, sccm Feed Temp., ° C. 15 15 Recycle Ratio 17 10 Polymer split,49.2 50.8 weight % Residence time, min. 19 10 Catalyst Type ConstrainedGeometry Heterogeneous Catalyst system Ziegler-Natta Titaniumcoordination catalyst system Catalyst efficiency, 2.0 0.3 MM lbs.product/lb. Titanium Volumetric Heat 400 630 Removal rate, BTU/hr *ft³ * ° F. Production rate, 132 137 (269) lbs./hr. (overall)

Table 2 provides the physical properties of Inventive Examples 1 and 2and comparative examples 3, 4 and 5.

TABLE 2 Property Inv. Ex. 1 Inv. Ex. 2 Comp. Ex. 3† Comp. Ex. 4† Comp.Ex. 5† Melt Index, I₂, g/10 min. 0.8 0.5 1.0 1.03 0.85 I₁₀/I₂ 7.4 7.27.8 9.96 7.4 Composition Density, g/cc 0.921 0.921 0.920 0.918 0.920 GPCM_(w) 133,500 145,500 130,700 80,400 116,800 GPC M_(n) 47,100 49,70034,300 38,467 34,900 M_(w)/M_(n) 2.83 2.93 3.81 2.09 3.35 ATREFT_(peak1,) ° C. 81.5 82 85 82.5 72 ATREF M_(v1) 94,400 118,900 100,00097,724 158,500 ATREF T_(peak2,) ° C. 98 98 98 None 98 ATREF M_(v2)158,500 167,900 149,600 NA 102,330 ATREF High Density Fraction, % 1422.2 15.9 0.5 20 M_(v1)/M_(v2) 0.60 0.71 0.67 NA 1.55 T_(peak2) −T_(peak1,) ° C. 16.5 16 13 NA 26 First Reactor Polymer Split, % 49.251.8 NA NA 36.8 *1st Reactor Polymer Density, g/cc 0.913 0.910 NA NA0.902 *1st Reactor Polymer I₂, g/10 min. 1.0 0.38 NA NA 0.19 *1stReactor Polymer M_(w) 97,400 127,900 NA NA 158,300 *1st Reactor PolymerLCB/10000 C. 0.13 0.08 NA NA 0.044 *2nd Reactor Polymer Density, g/cc0.929 0.933 NA NA 0.931 *2nd Reactor Polymer I₂, g/10 min. 0.4 0.6 NA NA2.4 *2nd Reactor Polymer M_(w) 149,700 135,900 NA NA 92,635 1stM_(w)/2nd M_(w) Density 0.65 0.94 NA NA 1.71 Differential (2nd − 1st)0.016 0.023 NA NA 0.029 †Comparative example provided for purposes ofcomparison only; not an example of the present invention. *Valuepredicted based on a kinetic model although a mass balance model wouldalso suffice where direct measurement is not convenient.

Nominal 50 mm blown film was fabricated from Inventive Example 1 and 2and comparative compositions 3, 4 and 5 on an Egan blown film unitequipped with 2 inch diameter, 32:1 L/D extruder and a 3 inch annulardie. The blown film extrusion conditions for each example is provided inTable 3.

TABLE 3 Example Inv. Ex 1 Inv. Ex 2 Comp. Ex 3† Comp. Ex 4† Comp. Ex 5†Die Gap, mils 35 35 35 35 35 Melt Temperature, ° F. 453 462 450 450 450Die Pressure, psi 5,870 6,210 5,040 3,270 5,430 Output, lbs./hr. 120 90120 >120*   120 Extruder Amperage 93 86 80 65 83 Blow-Up Ratio 2.7:12.7:1 2.7:1 2.7:1 2.7:1 †Comparative example provided for purposes ofcomparison only; not an example of the present invention. *Value is anestimate, not an actual measurement.

During the actual blown film fabrication, all of the examples exhibitedgood bubble stability. However, surprisingly, although InventiveExamples 1 and 2 are characterized by substantially higher molecularweights and narrower molecular weight distributions relative tocomparative example 3, the inventive examples exhibited comparableextrusion processibility; that is, the extrusion amperage for theinventive examples was only about 8 to about 16 percent higher than thatfor comparative example 3. This result is unexpected and surprisingbecause typically narrower molecular weight distributions and highermolecular weights are both well-known contribute to poor processabilitycharacteristics.

Table 4 lists film performance properties for Inventive Examples 1 and 2and comparative examples 3, 4 and 5.

TABLE 4 Example Inv. Ex 1 Inv. Ex 2 Comp. Ex 3† Comp. Ex 4† Comp. Ex 5†Dart Impact (Method B), g 530 760 236 324 800 Elmendorf Type A - MD, g570 538 691 526 510 Elmendorf Type A - CD, g 701 579 819 768 725Elmendorf MD/CD 0.81 0.93 0.84 0.68 0.70 Ultimate Tensile - MD, psi7,340 8,189 6,525 6,787 6,700 Ultimate Tensile - CD, psi 7,706 7,5725,480 6,139 6,350 Ultimate Tensile MD/CD 0.95 1.08 1.19 1.11 1.06Percent Film Haze 8.27 8.25 11.0 8.30 11.5 Elmendorf tear resistance wasdetermined in accordance with ASTM D1922. Ultimate tensile wasdetermined in accordance with ASTM D638. Percent film haze wasdetermined in accordance with ASTM D1003. †Comparative example providedfor purposes of comparison only; not an example of the presentinvention.

Table 4 indicates that Inventive Examples 1 and 2 exhibit an excellentbalance of performance properties. The inventive examples arecharacterized by balanced tear resistance, high and balanced ultimatetensile strength, high dart impact resistance and reduced film haze. By“balanced tear resistance” it is meant that the ratio of MD tear to CDtear is in the range of from about 0.8 to about 1. By “balanced ultimatetensile strength” it is meant that the ratio of MD ultimate tensilestrength to CD ultimate tensile strength is in the range of from about0.9 to about 1.1. By “high dart impact resistance” it is meant that at a0.908 g/cc density and 0.5 I₂, impact resistance would be ≧750 grams; ata 0.920 g/cc density and 0.5 I₂≧500 grams; and at a 0.926 g/cc densityand 0.5 I₂≧250 grams. More particularly, since dart impact resistance isrecognized to vary with density and melt index, high dart impactresistance is defined as a dart impact resistance (as determined inaccordance with Method B) equal to or greater than the product of theequation:dart impact resistance=2181621.3×den −1203704.2×den ²−273.7×LogI₂−987852.9where den is composition density (in g/cm³); den² is composition densitysquared and I₂ is melt index in accordance with ASTM D-1238, Condition190° C./2.16 kg.

Surprisingly, the inventive examples exhibit reduced film haze eventhough they are characterized by higher molecular weight and largerATREF temperature differential than comparative example 3. Even moresurprisingly, Table 3 indicates that the film haze of the inventiveexamples is unexpectedly equivalent to comparative example 4 which is ahomogeneously branched substantially linear ethylene polymer whichcharacterized by a more uniform compositional distribution, no highdensity polymer fraction, lower molecular weight and narrower molecularweight distribution, which are characteristics that are well-known toconfer to improved optical properties.

In a second evaluation, polymer compositions having a nominal 0.926 g/cccomposition density were compared. Table 5 shows the physical propertiesof the polymer compositions (Inventive Example 6 and comparativeexamples 7 and 8).

TABLE 5 Property Inv. Ex. 6 Comp. Ex. 7^(†) Comp. Ex. 8^(†) Melt Index,I₂, 0.5 0.85     1.04 g/10 min. I₁₀/I₂ 7.2 7.4     8.06 Composition0.926 0.926     0.9278 Density, g/cc GPC M_(w) 147,900 119,900 115,000‡GPC M_(n) 52,100 35,900  31,080‡ M_(w)/M_(n) 2.84 3.34     3.7 ATREFT_(peak1,) 87.5 75    87.5 ° C. ATREF M_(v1) 118,900 149,600 100,000‡ATREF T_(peak2,) 98 98    97 ° C. ATREF M_(v2) 166,000 100,00 150,000‡ATREF High 27.1 45.9    25.0 Density Fraction, % M_(v1)/M_(v2) 0.72 1.5    0.67 T_(peak2) − T_(peak1), 10.5 23     9.5 ° C. First Reactor 50.739.5 NA Polymer Split, % *1st Reactor 0.918 0.906 NA Polymer Density,g/cc *1st Reactor 0.35 0.17 NA Polymer I₂, g/10 min. *1st Reactor126,700 161,200 NA Polymer M_(w) *1st Reactor 0.09 0.076 NA PolymerLCB/10000C *2nd Reactor 0.934 0.939 NA Polymer Density, g/cc *2ndReactor 0.6 2.3 NA Polymer I₂, g/10 min. *2nd Reactor 133,400 92,936 NAPolymer M_(w) 1st M_(w)/2nd M_(w) 0.95 1.73 NA Density Differential0.016 0.033 NA (2nd − 1st) ^(†)Comparative example provided for purposesof comparison only; not an example of the present invention. *Valuepredicted based on a kinetic model. ‡Typical value.

Nominal 50 mm blown film was fabricated from Inventive Example 1 and 2and comparative compositions 3, 4 and 5 on an Egan blown film unitequipped with 2 inch diameter, 32:1 LID extruder and a 3 inch annulardie. The blown film extrusion conditions for each example is provided inTable 6.

TABLE 6 Example Inv. Ex 6 Comp. Ex 7^(†) Comp. Ex 8^(†) Die Gap, mils 3535 35 Melt Temperature, ° F. 460 468 462 Die Pressure, psi 6,280 6,1705,160 Output, lbs./hr. 90 120 120 Extruder Amperage 85 81 71 Blow-UpRatio 2.7:1 2.7:1 2.7:1 ^(†)Comparative example provided for purposes ofcomparison only; not an example of the present invention.

During the actual blown film fabrication, all of the examples exhibitedgood bubble stability. Table 7 lists film performance properties forInventive Example 6 and comparative examples 7 and 8. Surprisingly,during blown film fabrication, Inventive Example 6 exhibited fairprocessability (nominal amperage) even though the novel composition wascharacterized by a substantially higher molecular weight and a narrowermolecular weight distribution relative to comparative examples 7 and 8.

TABLE 7 Example Inv. Ex 6 Comp. Ex 7^(†) Comp. Ex 8^(†) Dart Impact(Method B), g 250 410 177 Elmendorf Type A - MD 570 456 477 ElmendorfType A - CD 627 803 718 Elmendorf MD/CD 0.91 0.57 0.66 UltimateTensile - MD, psi 6,785 6,820 6,975 Ultimate Tensile - CD, psi 6,8567,006 4,800 Ultimate Tensile MD/CD 0.99 0.97 1.45 Percent Film Haze10.27 14.0 12.0 Elmendorf tear resistance was determined in accordancewith ASTM D1922. Ultimate tensile was determined in accordance with ASTMD638. Percent film haze was determined in accordance with ASTM D1003.^(†)Comparative example provided for purposes of comparison only; not anexample of the present invention.

Table 7 indicates that Inventive Example 6 exhibits an excellentproperty balance. Relative to both comparative example 7 and 8,Inventive Example 6 exhibited superior tear resistance balance (cf. 0.91versus 0.66 and 0.57). Also, the inventive example had superior tensilestrength balance relative to comparative example 8 which is aheterogeneously branched ethylene/1-octene copolymer manufactured asdescribed above with a Ziegler-Natta catalyst system.

Additionally, similar to the results shown for Inventive Examples 1 and2, Table 7 indicates that Inventive Example 6 also exhibits surprisinglyimproved optical properties. The percent film haze of Inventive Example6 was lower that the comparative examples 7 and 8 even though theinventive example possessed are substantially higher molecular weight asindicated by I₂ melt index values.

In another evaluation designed to further investigate the requirementsfor improved processability, good optical properties and improvedtoughness, several inventive examples and comparative examples wereprepared. Table 8 provides the physical properties for the variouspolymer compositions which all have a nominal 0.921 g/cm³ compositiondensity.

Inventive Examples 9 and 10 and comparative examples 11 and 12 were allprepared using a process system and conditions similar to InventiveExample 1 (i.e. a constrained geometry catalyst system was feed to thefirst reactor of a two-reactor polymerization system and a conventionalZiegler catalyst system was feed to the second reactor). Comparativeexample 13 was made in a single reactor polymerization system undercontinuous solution polymerization conditions using a Ziegler-NattaMgCl₂ supported Titanium catalyst system having a high Mg:Ti molar ratioand a high Mg surface area.

Table 9 provides the performance properties for the Inventive Examples 9and 10 and comparative examples 11-13 as compared to Inventive Example 1and comparative examples 3 and 5.

TABLE 8 Inv. Inv. Comp. Comp. Comp. Property Ex 9 Ex 10 Ex 11† Ex 12† Ex13† Melt index, I₂, g/10 min. 0.87 0.76 0.83 0.8 1.02 I₁₀/I₂ 7.6 6.9 8.18.8 7.6 Composition Density, g/cc 0.9204 0.921 0.9219 0.9221 0.9201 GPCMw 125,000 123,000 132,300 115,600 125,400 GPC Mn 49,400 44,600 35,40023,000 35,800 Mw/Mn 2.53 2.76 3.74 5.03 3.50 ATREF Tpeak₁, C. 86 86 8689 85 ATREF M_(v1) 89,500 99,900 137,000 191,000 89,900 ATREF Tpeak₂, C.99 99 99 99 98 ATREF M_(v2) 104,000 101,000 59,000 89,300 129,000 ATREFHigh Density Fraction, % 15.3 15.5 9.4 8.4 12.4 M_(v1)/M_(v2) 0.86 0.992.32 2.14 0.70 Tpeak₂ − Tpeak₁, ° C. 13 13 13 10 13 First ReactorPolymer Split, % 51 50 56 52 NA *1st Reactor Polymer Density, g/cc 0.9130.913 0.913 0.910 NA *1st Reactor Polymer I₂, g/10 min. 0.6 0.4 0.2 0.2NA *1st Reactor Polymer Mw 112,100 125,500 143,400 149,300 NA *1stReactor Polymer LCB/10,000 C. 0.20 0.09 0.08 0.09 NA *2nd ReactorPolymer Density, g/cc 0.928 0.929 0.934 0.935 NA *2nd Reactor PolymerI₂, g/10 min. 0.9 1.3 25 21 NA *2nd Reactor Polymer Mw 120,100 109,00048,900 51,300 NA 1st Mw/2nd Mw 0.93 1.15 2.93 2.91 NA DensityDifferential (2nd − 1st) 0.015 0.015 0.021 0.025 NA †Comparative exampleprovided for purposes of comparison only; not an example of the presentinvention. *Value predicted based on a kinetic model.

TABLE 9 Inv. In. Inv. Comp. Comp. Comp. Comp. Comp. Property Ex 1 Ex 9Ex 10 Ex 11† Ex 12† Ex 13† Ex 3† Ex 5† Melt Index, I₂, (g/10 min.) 0.800.84 0.76 0.83 0.80 1.02 0.95 0.86 Composition Density (g/cc) 0.9210.920 0.921 0.922 0.922 0.920 0.920 0.920 I₁₀/I₂ 7.48 7.53 6.90 8.098.81 7.58 7.90 7.57 M_(w)/M_(n) 2.94 2.53 2.76 5.10 5.03 3.50 3.87 3.34Vicat Softening Point (° C.) 107.5 108.0 108.8 106.7 104.7 104.2 105.1105.8 Extruder Amps 94 88 94 76 66 78 80 86 Extruder Die Pressure (psi)6150 5780 6030 4860 4230 4600 4840 5320 Avg Haze Value, % 7.4 7.6 7.311.6 13.7 7.9 10.8 10.5 DART (Method B), grams 544 472 550 452 250 274266 646 Avg Elmendorf Type A CD, gms 806 909 802 758 765 702 885 862 AvgElmendorf Type A MD, gms 550 544 562 480 512 883 626 467 Type A MD/CD0.68 0.60 0.70 0.63 0.67 1.26 0.71 0.54 Avg Elmendorf Type B CD, gms1102 1139 1056 1091 1235 1165 1082 960 Avg Elmendorf Type B MD, gms 754718 747 674 667 877 781 598 Type B MD/CD 0.68 0.63 0.71 0.62 0.54 0.750.72 0.62 CD-Avg Ultimate Tensiles, psi 5885 6550 6630 6191 5013 56574978 5810 MD-Avg Ultimate Tensiles, psi 6383 7223 6791 6872 5972 72076289 7065 Ultimate Tensiles MD/CD 1.08 1.10 1.02 1.11 1.19 1.27 1.261.22 HSIT, ° C. ˜101 ˜102 ˜101 ˜105 ˜110 ˜101 ˜100 ˜100 HTIT, ° C. ˜102˜103 ˜102 ˜110 ˜116 ˜103 ˜101 ˜101 Note: 2 mil blown film. HSIT denotesheat seal initiation temperature. HTIT denotes hot tack initiationtemperature. †Comparative example provided for purposes of comparisononly; not an example of the present invention.

The data in Table 9 indicates that Inventive Example 9 exhibits improvedprocessability with improved optical properties while maintaining a highdart impact resistance. Comparative examples 11 and 12 which aretwo-component (polymer) compositions show improved processability;however, their optical properties were objection and their sealingproperties were poor (i.e. characterized as having initiationtemperatures higher than their Vicat Softening Point temperatures)rendering they inferior choices for use in, for example, laminating filmapplications.

In another evaluation, compositions with densities in the range of fromabout 0.91 to about 0.918 g/cm³ were investigated. Table 10 provides thephysical properties for these compositions.

Inventive Example 14 and comparative examples 17-20 were all made usinga process system and conditions similar to Inventive Example 1.Comparative examples 17-20 are cast film compositions made in accordancewith the teachings in WO 97/26000 and are sold as developmental productsby The Dow Chemical Company. Comparative examples 15 and 16 were bothmade in a single reactor polymerization system under continuous solutionpolymerization conditions. Comparative example 15 was made using aconventional TiCl Ziegler Natta catalyst system and comparative example16 was made using a constrained geometry catalyst system as described inU.S. Pat. Nos. 5,272,236; 5,278, 272; and 5,665,800.

Table 11 provides the performance properties for three of thecompositions, Inventive Example 14 and comparative examples 15 and 16.Table 11 shows that relative to comparative example 16, InventiveExample 14 exhibits improved toughness balance with good opticalproperties and heat sealability. Relative to comparative example 15,Table 11 also shows that Inventive Example 14 exhibits comparableproperty balance with significantly improved impact resistance, opticsand heat sealability. Further, it is contemplated that theprocessability of the Inventive Example 14 can be efficiently improvedby increasing its long chain branching content while maintaining itsother key improvement as exemplified or embodied, for example, inInventive Example 9.

TABLE 10 Inv. Comp. Comp. Comp. Comp. Comp. Comp. Property Ex 14 Ex 15†Ex 16† Ex 17† Ex 18† Ex 19† Ex 20† Melt index, I₂, g/10 min. 0.86 0.970.96 2.3 5 3.5 4 I₁₀/I₂ 7.1 8.2 10.4 6.6 6.6 6.6 6.6 CompositionDensity, g/cc 0.9101 0.9126 0.9104 0.917 0.918 0.915 0.916 GPC Mw120,600 116,600 86,100 95,900 75,600 81,400 ND GPC Mn 43,500 31,20038,000 37,700 27,700 33,600 ND Mw/Mn 2.77 3.74 2.27 2.54 2.73 2.42 <3.3** ATREF T_(peak1), ° C. 74 76.5 78 78 79 76 75 ATREF M_(v1)109,000 74,500 65,800 78,300 86,900 64,400 53,700 ATREF T_(peak2), ° C.99 99 None 99 99 99 99 ATREF M_(v2) 142,000 140,000 NA 109,000 86,10098,600 69,200 ATREF High Density 10.7 10.6 0 14.7 10.3 12.6 12.2Fraction, % M_(v1)/M_(V2) 0.77 0.53 NA 0.72 1.01 0.65 0.78 T_(peak2) −T_(peak1), ° C. 25 22.5 NA 21 20 23 24 First Reactor Polymer Split, % 51NA NA 51 51 51 51 *1st Reactor Polymer Density, g/cc 0.900 NA NA 0.9110.912 0.909 0.9096 *1st Reactor Polymer I₂, g/10 min. 0.3 NA NA 1 2.21.8 1.9 *1st Reactor Polymer M_(w) 141,400 NA NA 98,600 80,600 86,100 ND*1st Reactor Polymer LCB/10,000 C. 0.05 NA 0.077 0.077 0.077 ND *2ndReactor Polymer Density, g/cc 0.921 NA NA 0.923 0.924 0.921 0.9225 *2ndReactor Polymer I₂, g/10 min. 5 NA NA 2.9 6.5 4 5 *2nd Reactor PolymerM_(w) 76,000 NA NA 87,900 70,400 80,300 ND 1st M_(w)/2nd M_(w) 1.86 NANA 1.12 1.14 1.07 ND Density Differential (2nd − 1st) 0.021 NA NA 0.0120.012 0.012 0.0129 †Comparative example provided for purposes ofcomparison only; not an example of the present invention. *Valuepredicted based on a kinetic model. **Value is an estimate, not anactual measurement.

TABLE 11 Inv. Ex Comp. Ex Comp. Ex Performance Properties 14 15^(†)16^(†) Melt Index, I₂, (g/10 min) 0.86 0.97 0.96 Composition Density(g/cc) 0.910 0.913 0.910 I₁₀/I₂ 7.08 8.16 10.35 Vicat Soft. Pt. (° C.)94.7 94.1 96.7 Extruder Amps 97 75 73 Extruder Die Pressure (psi) 53604430 3820 Avg Haze Value, % 3.8 7.1 2.4 Dart B, g >850 610 >850 ModifiedDart, g >1470 776 1297 Avg Elmendorf Type A CD, g 822 904 685 AvgElmendorf Type A MD, g 621 715 408 Type A MD/CD 0.75 0.79 0.60 AvgElmendorf Type B CD, g 858 992 821 Avg Elmendorf Type B MD, g 621 862477 Type B MD/CD 0.72 0.87 0.58 CD-Avg Ultimate Tensiles, psi 8163 6322ND MD-Avg Ultimate Tensiles, psi 6676 4731 ND Ultimate Tensiles MD/CD0.82 0.75 ND HSIT, ° C. ˜82-83 ˜92-93 ˜82-83 HTIT, ° C. ˜90 ˜110 ˜93Note: 2 mil blown film. HSIT denotes heat seal initiation temperature.HTIT denotes hot tack initiation temperature. ^(†)Comparative exampleprovided for purposes of comparison only; not an example of the presentinvention.

In another evaluation, compositions with densities in the range of fromabout 0.929 to about 0.941 g/cm³ were investigated. Table 12 providesthe physical properties for these compositions and Table 13 provides theperformance properties for the compositions. Inventive Examples 22-24and comparative example 27 were all made using a process system andpolymerization conditions similar to the employed for InventiveExample 1. Comparative examples 25 and 26 were made using a singlereactor system under continuous solution polymerization conditions.Comparative example 25 was made using a conventional TiCl Ziegler Nattacatalyst system. Comparative example 26 was made using a Ziegler-NattaMgCl₂ supported Titanium catalyst system having a high Mg:Ti molar ratioand a high Mg surface area.

TABLE 12 Inv. Inv. Comp. Comp. Comp. Comp. Property Ex 22 Ex 23 Ex 24 Ex25 Ex 26 Ex 27 Melt index, I₂, g/10 min. 0.79 0.94 0.67 1.03 0.81 2.3I₁₀/I₂ 7.5 7.1 8.2 7.8 8.2 7.4 Composition Density, g/cc 0.9295 0.93050.9328 0.9304 0.9305 0.9409 GPC M_(w) 125,100 128,100 127,600 120,200116,300 92,100 GPC M_(n) 46,700 43,000 25,800 33,100 27,400 35,100M_(w)/M_(n) 2.68 2.98 4.95 3.63 4.24 2.62 ATREF T_(peak1), ° C. 90 94 9492 94 89 ATREF M_(v1) 86,400 144,000 141,000 120,000 91,100 79,400 ATREFT_(peak2), ° C. 99 None None 97 98 100 ATREF M_(v2) 97,000 NA NA 157,000110,000 75,700 ATREF High Density Fraction, % 81.3 79.7 75.6 70.7 65.860.3 M_(v1)/M_(v2) 0.89 NA NA 0.76 0.83 1.05 T_(peak2) − T_(peak1), ° C.9 NA NA 5 4 11 First Reactor Polymer Split, % 49 53 59 NA NA 29 *1stReactor Polymer Density, g/cc 0.923 0.928 0.925 NA NA 0.924 *1st ReactorPolymer I₂, g/10 min. 0.5 0.5 0.25 NA NA 0.8 *1st Reactor Polymer M_(w)111,300 109,800 134,000 NA NA 96,300 *1st Reactor Polymer LCB/10,000 C.0.53 0.17 0.15 NA NA 0.47 *2nd Reactor Polymer Density, g/cc 0.936 0.9340.945 NA NA 0.948 *2nd Reactor Polymer I₂, g/10 min. 0.9 1.3 60 NA NA2.6 *2nd Reactor Polymer M_(w) 120,000 108,200 38,500 NA NA 90,000 1stM_(w)/2nd M_(w) 0.93 1.01 3.48 NA NA 1.07 Density Differential (2nd −1st) 0.014 0.006 0.020 NA NA 0.025 †Comparative example provided forpurposes of comparison only; not an example of the present invention.*Value predicted based on a kinetic model. **Value is an estimate, notan actual measurement.

TABLE 13 Inv. Ex Inv. Ex Comp. Ex Comp. Ex Performance Properties 22 2324^(†) 25^(†) Melt Index, I₂, 0.79 0.94 0.67 1.03 (g/10 min.)Composition Density 0.929 0.931 0.933 0.930 (g/cc) I₁₀/I₂ 7.45 7.07 8.157.83 Vicat Softening 117.5 120.2 117.6 115.6 Point (° C.) M_(w)/M_(n)2.68 2.98 4.95 3.63 Extruder Amps 89 89 82 77 Extruder Die 5750 57705490 4390 Pressure (psi) Avg Haze Value, % 14.2 11.5 11.6 9.6 DART(Method A), 272 264 272 234 grams DART (Method B), 186 152 172 112 gramsAvg Elmendorf Type 675 451 610 459 A CD, g Avg Elmendorf Type 294 210232 254 A MD, g Type A MD/CD 0.44 0.46 0.38 0.55 Avg Elmendorf Type 862850 738 542 B CD, g Avg Elmendorf Type 336 306 302 270 B MD, g Type BMD/CD 0.39 0.36 0.41 0.50 CD-Avg Ultimate 6352 6173 5573 5381 Tensiles,psi MD-Avg Ultimate 6545 6196 6074 5872 Tensiles, psi Ultimate Tensiles1.03 1.00 1.09 1.09 MD/CD HSIT, ° C. ˜115 ˜115 ˜115 ˜110 HTIT, ° C. ˜115˜114 ˜117 ˜110 Note: 2 mil blown film. HSIT denotes heat seal initiationtemperature. HTIT denotes hot tack initiation temperature.^(†)Comparative example provided for purposes of comparison only; not anexample of the present invention.

The data in Table 13 indicates that, surprisingly, Inventive Examples 22and 23 provide significantly improved toughness properties, especiallyrelative to comparative example 25, and comparable processability (i.e.similar amperage and die pressure) although their molecular weightdistributions are substantially narrower than the comparative examples.

1. A polymer composition comprising at least two ethylene polymercomponents, the first polymer component is a homogeneously branchedlinear ethylene polymer, wherein the composition is characterized ashaving: a) a M_(w)/M_(n) of less than or equal to 3.3, as determined bygel permeation chromatography (GPC), b) an I₁₀/I₂ in the range of fromgreater than 6.6 to about 8.2, as determined in accordance ASTM D-1238,Condition 190° C./2.16 kg and Condition 190° C./10 kg, c) a compositiondensity less than 0.945 gram/cubic centimeter, as determined accordingto ASTM-792, d) the first polymer component having a first viscosityaverage molecular weight, M_(v1), and the second polymer componenthaving a second viscosity average molecular, M_(v2), whereinM_(v1)/M_(v2) is less than or equal to 1, as determined using ATREF-DV,and e) a first ATREF peak temperature, T_(peak1), and a second ATREFpeak temperature, T_(peak2), corresponding to the at least twocomponents and as determined using analytical temperature rising elutionfraction (ATREF), wherein the temperature differential between T_(peak2)and T_(peak1), ΔT, decreases with increased composition density suchthat ΔT is less than 23° C. at composition densities of greater than orequal to 0.926 g/cm³ and is greater than 43° C. at composition densitiesless than or equal to 0.92 g/cm³.
 2. The composition of claim 1 whereinthe I₁₀/I₂ ratio is greater than or equal to 7.1, as determined inaccordance with ASTM D-1238, Condition 190° C./10 kg.
 3. The compositionof claim 1 further characterized as having a density differentialbetween the two components less than or equal to 0.028 g/cm³, asmeasured in accordance with ASTM D-792.
 4. The composition of claim 1wherein the M_(v1)/M_(v2) is in the range of from about 0.8 to about 1,as determined using an ATREF-DV technique.
 5. The composition of claim 1wherein at least one of the first polymer component or second polymercomponent is prepared using a homogeneous catalyst system.
 6. Thecomposition of claim 1, wherein the second polymer components is aheterogeneously branched ethylene polymer.
 7. The composition of claim 1wherein both the first and second polymer components are homogeneouslybranched ethylene polymers.
 8. The composition of claim 7 wherein atleast one of the homogeneously branched ethylene polymers is asubstantially linear ethylene polymer.
 9. The composition of claim 1,wherein the first component is present in the composition in an amountof at least 40 wt. %.
 10. The composition of claim 1, wherein the firstcomponent is present in the composition in an amount of at least 60-75wt. %.
 11. The composition of claim 1, wherein the first component ispresent in the composition in an amount of at least 65-70 wt. %.